1. Field of the Invention
Embodiments of the present disclosure relate to control systems and, in particular, to feedback control systems which modify motion control data so as to allow a controlled system to smoothly conform to physical constraints.
2. Description of the Related Art
An animated mechanical figure or robot is a movable object that is animated through the use of one or more electromechanical (e.g. electric, hydraulic, pneumatic, or similar) devices, which are generally referred to as “actuators”. At a fundamental level, the actuators translate control signals, also referred to as “motion control data” or “instruction data,” into motion, thereby animating the figure or robot. The manner in which each actuator moves is dictated by the instruction data, which defines target states for each actuator in the figure or robot to achieve. These states may include, but are not limited to, position, velocity, and acceleration states. The instruction data provided to each actuator are coordinated so as to allow the figure or robot to achieve a desired effect, such as simulating the appearance of a person engaging in a moving activity. Animated mechanical figures are used in a wide variety of applications, including in theme parks, in moving artistic works, and in animated commercial devices.
The instruction data preferably generate movements which stay within defined limits. In one aspect, position limits reflect that actuators possess a finite range of motion, and cannot adopt certain positions. In another aspect, velocity and acceleration limits reflect the finite limits on the speed with which the actuators can respond and the torque that the actuators can apply.
Failure of the instruction data to remain within these limits may result in undesirable effects. For example, instruction data outside the limits may: (a) describe a motion that the actuators are not able to physically realize, (b) describe a motion that may damage the physical system, and/or (c) describe a motion that may result in unplanned stopping, jerking, and/or vibration of the figure, detracting from the theatrical illusion provided by the figure and detracting from the viewer's experience in viewing the figure. Therefore, steps are generally taken to prevent actuators from attempting to reach states outside of these limits.
This situation is further complicated by the fact that manipulating the operation of a selected actuator to conform to a physical constraint will often require manipulating the operation of other actuators in the system. For example, in a robot with two feet on the ground, adjusting the instruction data that control the position of one knee will typically result in changes to the instruction data that control other actuators, such as those in the hips and/or other knee, in order to substantially prevent the robot from falling over or undergoing some other undesired motion.
This process of manipulating the operation of an actuator in response to a constraint is typically referred to as “clipping”. Conventionally, clipping often results in abrupt, high frequency movements or vibrations of the animated figure as the motion of the actuator is changed to comply with the constraint. A number of techniques are employed to reduce the detrimental effects of clipping. In one aspect, the motion of the actuator is subjected to a low pass filter, which substantially attenuates frequencies above a selected cutoff frequency, thereby inhibiting the high frequency movements typically associated with clipping. In another aspect, mechanical compliance is introduced into the system, resulting in a system that mechanically absorbs kinetic energy generally, such that when a constraint is encountered, less kinetic energy is available to be dissipated in the large vibrations having the unnatural appearance associated with clipping.